A microporous film having breathability is well known and used for various consumer products such as packaging film and absorbent articles. There are prior art which are directed to improvement of such a microporous film, such as U.S. Pat. No. 4,923,650 published on May 8, 1990. JP Patent publication 93/230252-A published on Sep. 7, 1993. JP Patent publication 96/225680-A published on Sep. 3, 1996. JP Patent publication 94/62794-B published on Aug. 17, 1994, JP Patent publication 95/231913-A published on Sep. 5, 1995. JP Patent publication 96/300436-A published on Nov. 19, 1996. JP Patent publication 96/300498-A published on Nov. 19, 1996. JP Patent publication 96/300499-A published on Nov. 19, 1996. JP Patent publication 96/300500-A published on Nov. 19, 1996, and JP Patent publication 87/167332-A published on Jul. 23, 1987. The microporous film described in these publications worked quite well as a backsheet of an absorbent article which requires breathability and liquid impermeability. There are also publications which are directed to a process for making a microporous film and the microporous film made by the process, such as U.S. Pat. No. 4,116.892 published on Sep. 26, 1978, U.S. Pat. No. 4,153,751 published on May 8, 1979. and U.S. Pat. No. 4,289.831 published on Sep. 15, 1981. These publication disclose processes using a process of stretching a material to make a microporous film. However, none of the publication disclose a microporous film having extensibility or a process to make a microporous film having extensibility so that a part of a microporous film is extensible. These publications are directed to a technology to make non-microporous film microporous, but not a technology to make a microporous film extensible.
Absorbent articles such as a sanitary napkin having a portion of extensibility are disclosed in prior art, such as PCT publication WO 97/12576 published on Apr. 10, 1997, PCT publication WO 96/12462 published on May 1, 1996, U.S. Pat. No. 5,389.094 published on Feb. 14, 1995 and U.S. Pat. No. 5,704,930 published on Jan. 6, 1998. In these disclosures, the flaps of the sanitary napkin are provided extensibility for relieving the stresses that develop in the flaps when the flaps are folded down and under a wearer's undergarment. The extensibility can be provided by a number of different processes. For example, the extensibility on the flaps can be provided by mechanically straining, corrugating, "ring-rolling", heating and deforming, subjecting portions of the flaps to compression between mating plates, and the like. These processes include the process of applying a strain to a material to mechanically and permanently deform the material. Extensibility on the material is provided by remaining permanent deformation on the material. Therefore, a degree of extensibility is determined by a degree of an applied strain. The more extensibility requires, the higher strain is applied to the material.
As described above, microporous films are commonly used for a breathable backsheet of an absorbent article. Microporous films typically comprise a blend of a thermoplastic polymer and an inorganic filler such as calcium carbonate. The blend undergoes pore formation upon stretching as the inorganic filler separates from the polymer due to stress concentration. The formation of micropores permits the film to be breathable allowing the passage of vapor through the micropores while retarding the passage of liquid. While microporous films have good breathability, microporous films have lower "strain at break" than an ordinary non-microporous film. Therefore, if microporous films are subjected to high strain beyond the strain at break of the microporous film for deformation to obtain extensibility of the microporous film, such high strain causes many visible pin holes in the area where the strain is applied.
Based on the foregoing, there is a need of improvement for an absorbent article comprising a microporous film. None of the existing art provides all of the advantages and benefits of the present invention.